A. Field of Invention
This application pertains to a device for tensioning the cord used for operating a roller blind or other similar window covering, and more particularly to a tensioning device that is adapted to adjust the tension automatically to adjust for changes in the physical characteristics of the cord.
B. Description of the Prior Art
Window coverings such as roller blinds, vertical and horizontal Venetian blinds, and so on, are typically operated by control cords that can be pulled in one direction or another. While many window coverings use a cord with two ends, systems are also popular that use a cord forming a closed loop. However, such systems are alleged ti be potentially dangerous to children. Therefore, interested organizations (such as the American National Standards Institute (ANSI) and the Window Covering Manufacturers Association (WCMA)) have developed a specification, in conjunction with the Consumer Products Safety Commission (CPSC), requiring such closed loop cord control systems to be secured by a tensioning device. The tensioning device is used externally of the window covering and is arranged so that it applies a tension in the cord within a predetermined range.
These tensioning devices are extremely effective in minimizing the danger to infants and young children resulting from the improper use of these cords. However, one problem with them is that during installation they must be carefully adjusted because if too much tension is applied, the window covering becomes difficult to operate and the additional stress on the window covering components results in a high wear and tear and reduced useful life. In fact, under certain conditions if the tension is high enough, the window covering may stop operating.
Strict instructions are normally provided to installers on how to install the window covering and the tensioning device. However, these instructions are frequently ignored, especially if the installer is the homeowner and not a professional.
A further problem in existing tensioning devices is that a high tension may develop after the tensioning device is installed due to changes in the physical characteristics of cord. For example, if the cord is made of knit or braided material, its fibers may shrink due to age, temperature and/or humidity changes, resulting in an increased tension.
In view of the disadvantages of the prior art, it is an objective of the present invention to provide a tensioning device that adjusts automatically to maintain tension in a continuous cord to a predetermined level.
A further objective is to provide a tensioning device that can be installed easily and quickly without requiring any special tools or techniques.
Yet another objective is to provide a tensioning device that does not require any extensive redesign, changes of components or other increased costs.
Other objectives and advantages of the invention shall become apparent from the following description.
Briefly, a tensioning device adapted to tension a cord loop of a window treatment apparatus includes a housing; a cord guide disposed in said housing and adapted to receive a portion of the cord loop; a biasing member adapted to bias said cord guide to apply tension on said cord loop; and locking means adapted to lock said cord guide in an installation position, said locking means being removable to allow said cord guide to tension said cord loop. The locking means includes a tab removably inserted into said cord guide. The tab may be a flexible tab extending through said housing and said cord guide. In one embodiment, rails defining a path of movement for said cord guide are disposed within said housing, the cord guide being adapted to shift up and down in the housing along the guide to selectively increase or decrease the tension on the cord loop.
In another embodiment, the cord guide includes a pulley rotatably disposed in said housing.
In another aspect of the invention, the tensioning device includes a housing having two housing portions; a cord guide movably disposed within said housing and adapted to receive a cord loop; a biasing spring coupled to said cord guide and adapted to apply a biasing force on said cord guide to thereby tension said cord loop; and a locking tab extending through said housing, said locking tab being constructed and arranged to lock said cord guide against movement during installation, said locking tab being removable to release said biasing spring.